The Collaborative International Dictionary of English v.0.48:

Barnburner \Barn"burn`er\, n. [So called in allusion to the
   fable of the man who burned his barn in order to rid it of
   rats.]
   1. A member of the radical section of the Democratic party in
      New York, about the middle of the 19th century, which was
      hostile to extension of slavery, public debts, corporate
      privileges, etc., and supported Van Buren against Cass for
      president in 1848; -- opposed to Hunker. [Political
      Cant, U. S.]
      [Webster 1913 Suppl.]

   2. an impressively successful or unusually good event.
      [informal] "The rock concert was a real barnburner."
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

barnburner
    n 1: someone who burns down a barn
    2: an impressively successful event; "the rock concert was a
       real barnburner"